Add validate function to String (SAM)

Author: Chris--A

hardware/arduino/sam/cores/arduino/WString.cpp

@@ -154,6 +154,13 @@ unsigned char String::reserve(unsigned int size)
 	return 0;
 }
 
+unsigned int String::validate( bool remainder )
+{
+	if( !remainder ) len = 0;
+	while( len < capacity && buffer[ len ] ) ++len;
+	return len;	
+}
+
 unsigned char String::changeBuffer(unsigned int maxStrLen)
 {
 	char *newbuffer = (char *)realloc(buffer, maxStrLen + 1);

hardware/arduino/sam/cores/arduino/WString.h

@@ -78,6 +78,15 @@ class String
 	// is left unchanged).  reserve(0), if successful, will validate an
 	// invalid string (i.e., "if (s)" will be true afterwards)
 	unsigned char reserve(unsigned int size);
+	
+	// If reserved data is modified externally using c_str()/&str[x] 
+	// this function will allow the contents to be validated and ready
+	// for use with the String functionality.
+
+	// If remainder is true, only the reserved buffer is validated (capacity - len bytes)
+	// If remainder is false, the entire buffer is re-validated.
+	unsigned int validate( bool remainder = false );
+	
 	inline unsigned int length(void) const {return len;}
 
 	// creates a copy of the assigned value.  if the value is null or